1. Field of the Invention
The present invention generally relates to Asynchronous Transfer Mode (ATM) layer cell processing apparatuses, and more particularly to an ATM layer cell processing apparatus which processes cells such as Operation Administration and Maintenance (OAM) cells in an ATM layer of an ATM which is used in a broadband Integrated Services Digital Network (ISDN).
2. Description of the Related Art
Processing of cells in the ATM layer primarily includes functions such as a Usage Parameter Control (UPC) function which monitors a quality of a network, and an OAM function which monitors, detects and notifies failures and also monitors a communication quality.
The UPC function monitors a flow of cells flowing into the network, and monitors whether or not a communication is being made by following a usage band declared by a user. A process such as adding a tag to the cell or discarding the cell is carried out with respect to the cell which flows into the network by exceeding the usage band.
On the other hand, the OAM function transfers special cells called the OAM cells, and monitors the failures, the communication quality or the like. The OAM cells include various types, such as a Loop Back (LB) cell which is used to monitor whether or not a connection is actually set, an Alarm Indication Signal (AIS) cell which is used to notify a transmission path or a failure of an equipment, a Remote Defect Indicator (RDI) cell which is used to notify a failure detection to a remote equipment, and a Performance Monitoring (PM) cell which is used to monitor a transfer delay time, the communication quality and the like of the network.
The ATM layer terminates these OAM cells, and an OAM cell processing block carries out processes for various kinds of failure notifications and monitorings depending on the types of OAM cells. In addition, the OAM cell processing block also carries out an ATM layer process to assemble and insert the OAM cells.
In a case where the OAM cell processing block is divided into a LB cell processing section, a PM cell processing section and the like for each of the types of OAM cells, the cell processing section for each type of OAM cell must make a reference to a cell type, an OAM type and a function type of the input cell, and judge whether the input cell is to be processed in the cell processing section or the cell is to be processed by another cell processing section.
The cell type, the OAM type and the function type of the input cell are identified by making a reference to a cell identification table and an OAM identification table, based on contents of header information and OAM cell information field (payload) of the input cell. FIG. 1 shows the contents of the cell identification table, and FIG. 2 shows the contents of the OAM identification table.
From the cell identification table shown in FIG. 1, the cell types including a Virtual Path (VP) OAM cell (for segment), a VP OAM cell (for end-end), a VC OAM cell (for segment), and a VC OAM cell (for end-end) are discriminated based on a Virtual Path Identifier (VPI), Virtual Path Identifier (VCI) and Payload Type Indication (PTI) in the header information of the input cell.
A “segment” refers to a passing point of the cell, which is included in connecting points in the network. On the other hand, an “end-end” refers to an equipment forming an end point which terminates the cell.
The VP OAM cell (for segment) is an OAM cell for use between VP switches. The VP OAM cell (for end-end) and the VC OAM cell (for segment) are OAM cells for use between switching systems. In addition, the VC OAM cell (for end-end) is an OAM cell for use between user equipments.
With respect to the cells which are discriminated as being the OAM cells based on the cell identification table shown in FIG. 1, a reference is made to the OAM identification table shown in FIG. 2. From this OAM identification table, the OAM cell types including the AIS cell, the RDI cell, a Continuity Check (CC) cell, the LB cell, a Forward PM cell, a Backward PM cell, a performance monitoring start/stop cell, and a connection confirmation start/stop cell are discriminated based on data contents of the OAM type and the function type in the OAM cell information field.
FIG. 3 is a functional block diagram showing a conventional ATM layer cell processing apparatus in which a plurality of OAM cell processors are provided series. In addition, FIG. 4 is a functional block diagram showing a conventional ATM layer cell processing apparatus in which a plurality of OAM cell processors are provide in parallel. In FIG. 4, those parts which are the same as those corresponding parts in FIG. 3 are designated by the same reference numerals.
In FIGS. 3 and 4, a UPC processor 31 includes a cell identifying section, and decodes the header information of the input cell. This UPC processor 31 has a function of carrying out the UPC with respect to the arriving cell for each VPI or VCI.
A plurality of OAM cell processors 32 are provided, and one OAM cell processor 32 is provided with respect to each OAM cell type. Each OAM cell processor 32 is provided with a cell identifying section and a processing subject judging section, and discriminates the cell types shown in FIG. 1 by decoding the header information of the input cell. If the input cell is an OAM cell, the OAM cell information field is decoded, so as to discriminate the OAM cell types shown in FIG. 2. In other words, the OAM cell types are discriminated to determine whether or not the input cell is the subject of the processing in the OAM cell processor 32, and a corresponding OAM processing is carried out if the input cell is the subject of the processing in this OAM cell processor 32.
A cell processing judging section 33 judges whether or not the OAM cell output from each OAM cell processor 32 is to be discarded or inserted into a cell highway. A judgement result of the cell processing judging section 33 is output to a discard and insert processor 34 together with each OAM cell. The discard and insert processor 34 discards the OAM cell or inserts the OAM cell in the cell highway, depending on the judgement result from the cell processing judging section 33.
But according to the conventional ATM layer cell processing apparatuses shown in FIGS. 3 and 4, the following problems occur.
First, in each OAM cell processor 32 which is provided with respect to a corresponding OAM cell type, it is necessary to provide the cell identifying section and the processing subject judging section which respectively carry out cell identification and OAM identification which are similar and overlap, with respect to one input cell. As a result, the construction and the processing within the OAM cell processor 32 are complex, thereby increasing both the scale and the processing delay of the ATM layer cell processing apparatus.
Second, it is essential to provide the cell processing judging section 33 which collects the processed results of the OAM cell processors 32 which are provided with respect to each of the OAM cell types, and finally determines the discard or insert process with respect to the OAM cells.
Third, when the OAM cell processors 32 are to be operated in parallel, the cell identifying sections and the processing subject judging sections within the plurality of OAM cell processor 32 are operated simultaneously when the cell arrives, thereby increasing the power consumption of the ATM layer cell processing apparatus.